Chemistry of a new family of aryl ruthenium species incorporating α-diimine chelation and a pendant imine-phenol function

Abstract

The reaction of excess 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) with Ru(η 2-RL)(PPh 3) 2(CO)Cl ( 1) has respectively furnished [Ru(η 1-RL)(PPh 3) 2(CO)(bpy)](PF 6) ( 2) and [Ru(η 1-RL)(PPh 3) 2(CO)(phen)](PF 6) ( 3) in very good yield (η 2-RL is C 6H 2O-2-CHNHC 6H 4R( p)-3-Me-5, η 1-RL is C 6H 2OH-2-CHNC 6H 4R( p)-3-Me-5 and R is H, Me, MeO, Cl). The chelation of bpy/phen is attended with the cleavage of RuO and RuCl bonds and iminium-phenolato→imine-phenol prototropic shift. The carbon monoxide ligand is located syn to the phenolic oxygen in 2 and 3 as opposed anti in 1. The crystal and molecular structures of [Ru(η 1-HL)(PPh 3) 2(CO)(bpy)](PF 6)·CH 2Cl 2 ( 2(H)·CH 2Cl 2) and [Ru(η 1-ClL)(PPh 3) 2(CO)(phen)](PF 6)·H 2O ( 3(Cl)·H 2O) are reported. In the lattice of 3(Cl)·H 2O, the water molecules form dimers (O⋯O, 2.617(8) Å). In the hydrogen bonded imine-phenol function the N⋯O distance is 2.550(9) Å in 2(H)·CH 2Cl 2 and 2.581(7) Å in 3(Cl)·H 2O. The Rubpy fragment in 2(H)·CH 2Cl 2 along with the CO ligand and the metallated carbon atom define an equitorial plane from which the metallated aldimine fragment (pendant Ph excluded) is rotated by 39.1° due to interligand repulsion and the two RuP distances (2.384(3) and 2.456(3) Å) become significantly different. The repulsion also counteracts the trans influence of the metallated carbanionic site, the RuN bond trans to the site being shorter. The behaviour of 3(Cl)·H 2O is similar. In dichloromethane solution 2 and 3 display a quasireversible Ru III/Ru II cyclic voltammetric response with E 1/2 in the range 0.75–0.85 V versus SCE. The CO stretch in 2 and 3 is 30–40 cm −1 higher than that in 1 due to the presence of dπ(Ru)–pπ(bpy/phen) back-bonding. The corresponding MLCT absorption ( λ max, ∼470 nm) gives rise to fluorescence ( λ max, ∼540 nm). The reaction of 2-(2-pyridyl)benzthiazole (pbt) with 1 has furnished [Ru(η 1-RL)(PPh 3) 2(CO)(pbt)](PF 6) ( 8) in which pbt is (N,N) chelated. The properties of 8 are generally similar to those of 2 and 3.